1. Field of the Invention
The present invention relates to a lighting device that is capable of guiding light outputted from a light source toward an object to be irradiated, such as an indicator of an instrument panel for a motor vehicle.
2. Description of the Related Art
A conventional lighting device of this kind is disclosed in Japanese patent laid-open publication No. 2003-130693. This conventional lighting device is used for illuminating an indicator of an instrument panel mounted on a motor vehicle for example, and is equipped with a light source for emitting light and a light guide body for guiding the light toward an indicator needle and an indicator plate with display designed parts, such as scale marks and characters, arranged around a center axis of the indicator needle for indicating a vehicle speed, an engine speed, a fuel remaining amount and others. The light source is arranged in the vicinity of a spindle of the indicator needle, and the light guide body is arranged between the indicator plate and the light source to receive and guide its light. The light body is made of transparent material and is formed with a first partially-conic surface for reflecting the light introduced from the light source in an outer radial direction and a second partially-conic surface, which is arranged outwardly in a radial direction and provided with crimps and the like, for reflecting and guiding the light reflected on the first partially-conic surface toward the indicator needle and the display plate so as to illuminate them.
Another conventional lighting device used for an instrument panel of a motor vehicle is known, and is illustrated in FIGS. 7A and 7B. This device includes a light source 7 and a light guide body consisting of a plurality of body portions 800. The body portions 800 are made of translucent material, each having an inner portion 800a and an outer portion 800b extending radially from the inner portion 800a, and are arranged to be in a partially-circular shape centered on a spindle 5 of a not-shown indicator needle. An inner-circumferential side surface 801 of the inner portion 800a and an outer-circumferential side surface 802 of the outer portion 800b are formed to have curved side surfaces, which are centered on a center axis 5a of the spindle 5. Specifically, the inner-circumferential side surface 801 of the inner portion 800a is shaped in concave when it is seen from a front side of the instrument panel. The inner portion 800a is thicker than the outer portion 800b and vertically bent so that its bottom surface can receive light outputted from the light source 7 and its upper curved surface can reflect light and change a vertical direction thereof toward a radially-outward direction. The outer portion 800b is slanted gradually in an upward direction, approaching eyes of a user, and becomes thinner from its inner portion toward its outer portion. Incidentally, display designed parts are arranged around the center axis 5a, but they are omitted in FIGS. 7A and 7b. 
The both conventional lighting devices, however, encounter a problem in that illumination efficiency and brightness of the display designed parts are decreased because of light deviating therefrom, consequently deteriorating visibility of the indicator and the display designed parts.
In the latter conventional lighting device, the light entered the light guide body is reflected by the inner portion 800b having the concave inner-circumferential side surface 801 centered on the center axis 5a of the spindle 5 as shown in FIG. 7A and the upper curved surface sharply bent in vertical cross-section as shown in FIG. 7B. The entered light is widely diffused by reflecting on these, surfaces from a central line L passing through the center axis 5a and the light source 7, because much part of the reflected light travels deviating from radial directions centered on the center axis 5a. The light, traveling in the outer portion 800b toward the outer-circumferential side surface 802, is reflected on both side surfaces thereof in various directions, and accordingly some of the light deviates from the display designed parts. The light reflected by a rear surface of the outer portion 800b is diffused in various directions so that an amount of the light going to eyes of a user is decreased, because the light which deviates from the radial directions to hit the rear surface is hard to reach the eyes of the user. This causes decrease in its efficiency of illuminating the display designed parts and the indicator.
In the former conventional lighting device, the light travels similarly to the latter conventional lighting device, which also causes the decrease in its illumination efficiency.
It is, therefore, an object of the present invention to provide a lighting device which overcomes the foregoing drawbacks and can increase an illuminating efficiency to improve visibility of the display designed parts to be illuminated.